Detection of scalar fields by Extreme Mass Ratio Inspirals with a Kerr black hole

TL;DR

This paper investigates how scalar fields influence gravitational wave signals from extreme mass ratio inspirals into Kerr black holes, highlighting potential observational signatures of modified gravity.

Contribution

It introduces a numerical framework to analyze scalar and tensor perturbations in EMRIs within modified gravity, emphasizing the impact of scalar charge on gravitational wave observables.

Findings

Scalar emission increases energy loss and reduces orbital cycles.

Higher black hole spin amplifies scalar charge effects on gravitational waves.

Scalar charge presence could be detectable through gravitational wave observations.

Abstract

We study extreme mass ratio inspirals occurring in modified gravity, for which the system is modeled by a small compact object with scalar charge spiraling into a supermassive Kerr black hole. Besides the tensorial gravitational waves arising from the metric perturbations, radiations are also induced by the scalar field. The relevant metric and scalar perturbations are triggered by the orbital motion of the small object, which give rise to a system of inhomogeneous differential equations under the adiabatic approximation. Such a system of equations is then solved numerically using Green's function furnished by the solutions of the corresponding homogeneous equations. To explore the present scenario from an observational perspective, we investigate how the pertinent observables are dependent on specific spacetime configurations. In this regard, the energy fluxes and the gravitational wave dephasing accumulated during the process are evaluated, as functions of the scalar charge, mass ratio, and spin of the central supermassive black hole. In particular, the presence of additional scalar emission leads to a more significant rate of overall energy loss, which, in turn, decreases the total number of orbital cycles before the small object plunges into the central black hole. Moreover, for a central black hole with a higher spin, the imprints of the scalar charge on the resultant gravitational radiations are found to be more significant, which indicates the possibility of detecting the scalar charge.